正Man's World

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(PI());
            Console.ReadLine();

        }
        static double PI()
        {
            double pi, t;
            int n, sign;

            n = 1;
            sign = 1;
            pi = 0;
            t = 0;

            do
            {
                t = 4.0 / ((2 * n) - 1);//if n=0,則為2n+1
                pi += t * sign;
                sign = -sign;
                n++;
            } while (t > 0.0000001);
            return pi;
        }

    }
}